The invention concerns a radio-controlled wristwatch which includes a magnetic longwave antenna received in the wristwatch casing.
A radio-controlled wristwatch of that kind, as is described for example in EP 0 896 262 A1 (corresponding to U.S. Ser. No. 09/131,668, the disclosure of which being incorporated herein by reference), has proven itself in practice. It is distinguished by virtue of its works being of an extremely compact structure because the ferrite bar antenna is flexible (i.e. formed of laminated plates) and follows (i.e., is parallel to) the inside contour of the casing, and is integrated into the printed circuit board with the processor for the electronic receiving, decoding and timing circuits. It will be noted however that a structure of that kind requires a non-metallic timepiece casing because otherwise the proximity of the metal to the antenna means that the antenna function would be impaired, to such an extent as to be inoperable, not only as a consequence of mistuning but in particular also as a consequence of quality losses which cannot be compensated by subsequent tuning.
If however for aesthetic reasons a metal timepiece casing is wanted, then the magnetic longwave antenna for receiving the encoded time information has to be moved to a position outside the casing, that is to say into the strap or bracelet of the wristwatch, as is described in greater detail for example in U.S. Pat. No. 5,144,599 (the disclosure of which being incorporated herein by reference). Such a structure developed as the standard almost a decade ago. It however suffers from the fundamental disadvantages that, by virtue of the fact of the wristwatch being worn on the wrist, there exists a serious risk of accelerated wear occurring at the place where the strap or bracelet abuts against the casing (because of the requirement for a flexible introduction of the antenna line) and also at the strap or bracelet itself (because of the admittedly flexible but nonetheless non-negligible foreign body in the form of the laminated ferrite antenna in the tubular strap or bracelet).
The object of the present invention is therefore that of combining the advantages of the previously known radio-controlled wristwatches having a plastic casing and an integrated antenna on the one hand, and radio controlled wristwatches with a metal casing and an external antenna on the other hand, which opens a new wide range of designs of high-quality timepieces with a high degree of comfort in terms of wearing the timepiece and a low level of susceptibility to trouble.
In accordance with the invention that object is essentially attained in that the radio-controlled wristwatch has a metal central portion in the region situated between the timepiece glass and an electrically non-conducting bottom, wherein a ferrite bar antenna is installed over its entire length at a not-inconsiderable radial spacing from the inside wall of the timepiece casing towards the center thereof.
For the case which is to be preferred for design construction reasons, where the magnetic longwave antenna is again arranged on the printed circuit board at the edge of the timepiece works, to ensure radial spacing in all directions of the antenna core relative to the inside wall of the electrically conducting central portion of the casing, a spacer ring injection-molded from plastic material is desirably fitted into the central portion of the casing, the spacer ring in turn serving in the center as a receiving ring for the works equipped with the ferrite bar. In that case, the expensive configuration of a laminated core which is fitted in a curved condition does not need to be selected for the ferrite bar, it is sufficient to install an inexpensive rigid prismatic bar along a secant relative to the periphery of the timepiece works, preferably with inclined ground-off ends, the bar being as long as possible to fit snugly in shape-locking relationship into the correspondingly recessed internal periphery of the spacer ring.
The non-metal bottom of the timepiece casing can comprise plastic or glass material. Glass may be preferable, because the surface of the glass which bears against the wrist is found to be extremely sympathetic and completely allergy-free in relation to the skin. If there is no wish to have the option of looking into the wristwatch works in the manner of a skeleton-type timepiece, as would be the case if the glass bottom were transparent, then the inside of the bottom glass can be provided with a non-metallic vapor deposition and thereby rendered opaque. In that case, in the course of the vapor deposition procedure, the bottom could be provided with an ornamental configuration, for example by means of figurative stencils; or the deposit could then be processed to afford a figurative configuration, by laser erosion (which produces processing tracks burnt black in the deposit, and which can also be effected subsequently from the exterior through the glass of the bottom when already fitted in place).